Abstract

The aerodynamic and acoustic characteristics of a generic hingeless coaxial helicopter with a tail-mounted propulsor and stabiliser have been simulated using Brown's Vorticity Transport Model. This has been done to investigate the ability of models of this type to capture the aerodynamic interactions that are generated between the various components of realistic, complex helicopter configurations. Simulations reveal the aerodynamic environment of the coaxial main rotor of the configuration to be dominated by internal interactions that lead to high vibration and noise. The wake of the main rotor is predicted to interact strongly with the tailplane, particularly at low forward speed, to produce a strong nose-up pitching moment that must be countered by significant longitudinal cyclic input to the main rotor. The wake from the main rotor is ingested directly into the tail propulsor over a broad range of forward speeds, where it produces significant vibratory excitation of the system as well as broadband noise. The numerical calculations also suggest the possibility that poor scheduling of the partition of the propulsive force between the main rotor and propulsor as a function of forward speed may yield a situation where the propulsor produces little thrust but high vibration as a result of this interaction. Although many of the predicted effects might be ameliorated or eliminated entirely by more careful or considered design, the model captures many of the aerodynamic interactions, and the resultant effects on the loading on the system, that might be expected to characterise the dynamics of such a vehicle. It is suggested that the use of such numerical techniques might eventually allow the various aeromechanical problems that often beset new designs to be circumvented - hopefully well before they manifest on the prototype or production aircraft.